Enhanced plasma mode and system for plasma immersion ion implantation

ABSTRACT

A novel plasma treatment method ( 800, 814 ). The method includes forming an rf plasma discharge in a vacuum chamber. The plasma discharge includes an inductive coupling structure, which has a first cusp region at a first end of the structure and a second cusp region at a second end of the structure. In some embodiments, a third cusp region, which is between the first and second cusp regions, can also be included. The first cusp region is provided by a first electro-magnetic source and the second cusp region is provided by a second-electro magnetic source. The first electro-magnetic source and the second electro-magnetic source confines a substantial portion of the rf plasma discharge to a region away from a wall of the vacuum chamber. Accordingly, a plasma discharge is substantially a single ionic species (e.g., H 1 +) can be formed.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The following five commonly-owned co-pending applications, includingthis one, are being filed concurrently and the other four are herebyincorporated by reference in their entirety for all purposes:

1. U.S. patent application Ser. No. 09/201,946 Wei Liu, et al.,entitled, “Enhanced Plasma Mode and System For Plasma Immersion IonImplantation,”;

2. U.S. patent application Ser. No. 09/203,025 Wei Liu, et al.,entitled, “Enhanced Plasma Mode and Method For Plasma Immersion IonImplantation,”;

3. U.S. patent application Ser. No. 09/201,933 Wei Liu, et al.,entitled, “Enhanced Plasma Mode and Computer System For Layer TransferProcesses,”;

4. U.S. Provisional Patent Application Ser. No. 60/110,378 Wei Liu, etal., entitled, “Enhanced Plasma Mode, Method, and System For DomedChamber Designs,”; and

5. U.S. Provisional Patent Application Ser. No. 60/110,528 Wei Liu, etal., entitled, “Enhanced Plasma Mode, Method, and System For ChamberDesigns,”.

BACKGROUND OF THE INVENTION

The present invention relates to the manufacture of objects. Moreparticularly, the present invention provides a technique for providing acombination of a plasma discharge and an applied magnetic field forcreating a high density plasma source. The present invention can beapplied to implanting particles for the manufacture of integratedcircuits, for example. But it will be recognized that the invention hasa wider range of applicability; it can also be applied to implantingparticles for other substrates such as multi-layered integrated circuitdevices, three-dimensional packaging of integrated semiconductordevices, photonic devices, piezoelectronic devices,microelectromechanical systems (“MEMS”), sensors, actuators, solarcells, flat panel displays (e.g., LCD, AMLCD), doping semiconductordevices, biological and biomedical devices, and the like.

Integrated circuits are fabricated on chips of semiconductor material.These integrated circuits often contain thousands, or even millions, oftransistors and other devices. In particular, it is desirable to put asmany transistors as possible within a given area of semiconductorbecause more transistors typically provide greater functionality, and asmaller chip means more chips per wafer and lower costs. Some integratedcircuits are fabricated on a slice or wafer, of single-crystal(monocrystalline) silicon, commonly termed a “bulk” silicon wafer.Devices on such “bulk” silicon wafer typically are made by processingtechniques such as ion implantation or the like to introduce impuritiesor ions into the substrate. These impurities or ions are introduced intothe substrate to selectively change the electrical characteristics ofthe substrate, and therefore devices being formed on the substrate. Ionimplantation provides accurate placement of impurities or ions into thesubstrate. Ion implantation, however, is expensive and generally cannotbe used effectively for introducing impurities into a larger substratesuch as glass or a semiconductor substrate, which is used for themanufacture of flat panel displays or the like.

Accordingly, plasma treatment of large area substrates such as glass orsemiconductor substrates has been proposed or used in the fabrication offlat panel displays or 300 millimeter silicon wafers. Plasma treatmentis commonly called plasma immersion ion implantation (“PIII”) or plasmasource ion implantation (“PSI”). Plasma treatment generally uses achamber, which has an inductively coupled plasma source, for generatingand maintaining a plasma therein. A large voltage differential betweenthe plasma and the substrate to be implanted accelerates impurities orions from the plasma into the surface or depth of the substrate. Avariety of limitations exist with the convention plasma processingtechniques.

A major limitation with conventional plasma processing techniques is themaintenance of the uniformity of the plasma density and chemistry oversuch a large area is often difficult. As merely an example, inductivelyor transformer coupled plasma sources (“ICP” and “TCP,” respectively)are affected both by difficulties of maintaining plasma uniformity usinginductive coil antenna designs. Additionally, these sources are oftencostly and generally difficult to maintain, in part, because suchsources which require large and thick quartz windows for coupling theantenna radiation into the processing chamber. The thick quartz windowsoften cause an increase in radio frequency (“rf”) power (or reduction inefficiency) due to heat dissipation within the window.

Other techniques such as Electron Cyclotron Resonance (“ECR”) andHelicon type sources are limited by the difficulty in scaling theresonant magnetic field to large areas when a single antenna or waveguide is used. Furthermore, most ECR sources utilize microwave power.Microwave power is often more expensive and difficult to tuneelectrically. Hot cathode plasma sources have been used or proposed. Thehot cathode plasma sources often produce contamination of the plasmaenvironment due to the evaporation of cathode material. Alternatively,cold cathode sources have also be used or proposed. These cold cathodesources often produce contamination due to exposure of the cold cathodeto the plasma generated.

A pioneering technique has been developed to improve or, perhaps, evenreplace these conventional sources for implantation of impurities. Thistechnique has been developed by Dr. Chung Chan of Waban Technology inMassachusetts, now Silicon Genesis Corporation, and has been describedin U.S. Pat. No. 5,653,811 (“Chan”), which is hereby incorporated byreference herein for all purposes. Chan generally describes techniquesfor treating a substrate with a plasma with an improved plasmaprocessing system. The improved plasma processing system, includes,among other elements, at least two rf sources, which are operative togenerate a plasma in a vacuum chamber. By way of the multiple sources,the improved plasma system provides a more uniform plasma distributionduring implantation, for example. It is still desirable, however, toprovide even a more uniform plasma for the manufacture of substrates.

From the above, it is seen that an improved technique for introducingimpurities into a substrate is highly desired.

SUMMARY OF THE INVENTION

According to the present invention, a technique including a method forproviding a high density plasma source is provided. In an exemplaryembodiment, the present invention provides a method that uses acombination of a high frequency source and a magnetic source to form ahigh density plasma. The high density plasma source can provide a plasmathat is substantially a single isotope of hydrogen, for example.

In a specific embodiment, the present invention provides a novel methodfor forming a plasma. The method includes forming an rf plasma dischargein a vacuum chamber. The plasma discharge includes an inductive couplingstructure, which has a first cusp region at a first end of the structureand a second cusp region at a second end of the structure. In someembodiments, a third cusp region, which is between the first and secondcusp regions, can also be included. The first cusp region is provided bya first electro-magnetic source and the second cusp region is providedby a second-electro magnetic source. The first electro-magnetic sourceand the second electro-magnetic source confines a substantial portion ofthe rf plasma discharge to a region away from a wall of the vacuumchamber. Accordingly, a plasma discharge is substantially a single ionicspecies can be formed.

In an alternative embodiment, the present invention includes a novelmethod for implanting particles using a plasma source. The methodincludes forming an rf plasma discharge in a vacuum chamber. The plasmadischarge includes an inductive coupling structure, which has a firstcusp region at a first end of the structure and a second cusp region ata second end of the structure. In some embodiments, a third cusp region,which is between the first and second cusp regions, can also beincluded. The first cusp region is provided by a first electro-magneticsource and the second cusp region is provided by a second-electromagnetic source. The first electro-magnetic source and the secondelectro-magnetic source confine a substantial portion of the rf plasmadischarge to a region away from a wall of the vacuum chamber. The methodalso includes biasing a substrate relative to the plasma discharge tointroduced particles from the plasma into the substrate. By way of theplasma discharge, which can be substantially a single ionic species(e.g., H₁+), a uniform distribution of implanted particles at a selecteddepth in the substrate is achieved.

Numerous benefits are achieved by way of the present invention. In oneaspect, the present invention provides a high density plasma source thatis rich with hydrogen bearing particles in the H₁+ state. This highdensity source is an active which allows the hydrogen bearing particlesto be implanted in a uniform manner through a surface of a substratesuch as a silicon wafer. In another aspect, the present inventionachieves a high density plasma source in a simple and elegant sourcedesign, which uses a lower amount of rf power than conventionalmulti-coil sources. The present invention also provides a method forigniting the plasma source in a “proton” state, which is highlyefficient. Depending upon the embodiment, one or more of these benefitsis present. These and other advantages or benefits are describedthroughout the present specification and are described more particularlybelow.

These and other embodiments of the present invention, as well as itsadvantages and features are described in more detail in conjunction withthe text below and attached FIGS.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a conventional plasma treatmentsystem;

FIGS. 2-7 are simplified diagrams of plasma treatment systems accordingto embodiments of the present invention;

FIGS. 8-8A are simplified diagrams of plasma treatment methods accordingto embodiments of the present invention; and

FIGS. 9-10 are simplified diagrams of experimental information accordingto embodiments of the present invention

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

According to the present invention, a technique including a method andsystem for providing a high density plasma source is provided. In anexemplary embodiment, the present invention provides an apparatus thatuses a combination of a high frequency source and a magnetic source toform a high density plasma. The high density plasma can provide a plasmathat is substantially a single isotope of hydrogen, for example.

1. Conventional Plasma Processing System

In brief overview and referring to FIG. 1, conventional plasmaprocessing system 10 includes a vacuum chamber 14 having a vacuum port18 connected to a vacuum pump (not shown). The system 10 includes aseries of dielectric windows 26 vacuum sealed by o-rings 30 and attachedby removable clamps 34 to the upper surface 22 of the vacuum chamber 14.Removably attached to some of these dielectric windows 26 are rf plasmasources 40, in a system having a helical or pancake antennae 46 locatedwithin an outer shield/ground 44. Cooling of each antenna isaccomplished by passing a cooling fluid through the antenna. Cooling istypically required only at higher power. The windows 26 without attachedrf plasma sources 40 are usable as viewing ports into the chamber 14.The removability of each plasma source 40 permits the associateddielectric window 26 to be cleaned or the plasma source 40 replacedwithout the vacuum within the system 10 being removed. Although glasswindows are used, other dielectric material such as quartz orpolyethylene may be used for the window material.

Each antenna 46 is connected to an rf generator 66 through a matchingnetwork 50, through a coupling capacitor 54. Each antenna 46 alsoincludes a tuning capacitor 58 connected in parallel with its respectiveantenna 46. Each of the tuning capacitors 58 is controlled by a signalD, D′, D″ from a controller 62. By individually adjusting the tuningcapacitors 85, the output power from each rf antenna 46 can be adjustedto maintain the uniformity of the plasma generated. Other tuning meanssuch as zero reflective power tuning may also be used to adjust thepower to the antennae. The rf generator 66 is controlled by a signal Efrom the controller 62. The controller 62 controls the power to theantennae 46 by a signal F to the matching network 50.

The controller 62 adjusts the tuning capacitors 58 and the rf generator66 in response to signals A, B, and C. Here, signal A is from a sensor70 monitoring the power delivered to the antennae 46. Signal B is from afast scanning Langmuir probe 74 directly measuring the plasma density.Signal C is from a plurality of Faraday cups 78 attached to a substratewafer holder 82. The Langmuir probe 74 is scanned by moving the probe(double arrow I) into and out of the plasma. With these sensors, thesettings for the rf generator 66 and the tuning capacitors 58 may bedetermined by the controller prior to the actual use of the system 10 toplasma treat a substrate. Once the settings are determined, the probesare removed and the wafer to be treated is introduced. The probes areleft in place during processing to permit real time control of thesystem. Care must be taken to not contaminate the plasma with particlesevaporating from the probe and to not shadow the substrate beingprocessed.

This conventional system has numerous limitations. For example, theconventional system 10 includes wafer holder 82 that is surrounded by aquartz liner 101. The quartz liner is intended to reduce unintentionalcontaminants sputtered from the sample stage to impinge or come incontact with the substrate 103, which should be kept substantially freefrom contaminates. Additionally, the quartz liner is intended to reducecurrent load on the high voltage modulator and power supply. The quartzliner, however, often attracts impurities or ions 104 that attachthemselves to the quartz liner by way of charging, as shown by FIG. 1A.By way of this attachment, the quartz liner becomes charged, whichchanges the path of ions 105 from a normal trajectory 107. The change inpath can cause non-uniformities during a plasma immersion implantationprocess. FIG. 1B shows a simplified top-view diagram of substrate 103that has high concentration regions 111 and 109, which indicatenon-uniformity. In some conventional systems, the liner can also be madeof a material such as aluminum. Aluminum is problematic in conventionalprocessing since aluminum particles can sputter off of the liner andattach themselves to the substrate. Aluminum particles on the substratecan cause a variety of functional and reliability problems in devicesthat are manufactured on the substrate. A wafer stage made of stainlesssteel can introduce particulate contamination such as iron, chromium,nickel, and others to the substrate. A paper authored by Zhineng Fan,Paul K. Chu, Chung Chan, and Nathan W. Cheung, entitled “Dose and EnergyNon-Uniformity Caused By Focusing Effects During Plasma Immersion IonImplantation,” published in “Applied Physics Letters” describes some ofthe limitations mentioned herein.

Additionally, the conventional system introduces ions 108 toward thesubstrate surface in a non-uniform manner. As shown, ions acceleratetoward the substrate surface at varying angles and fluxes. These varyingangles and fluxes tend to create a non-uniform ion distribution in thesubstrate material. The non-uniform distribution of ions in thesubstrate can create numerous problems. For example, a non-uniformdistribution of ions in a substrate used for a film transfer processsuch as Smart Cut™ or a controlled cleaving process can ultimatelycreate a non-uniform detached film, which is highly undesirable in themanufacture of integrated circuits. Accordingly, it is generallydesirable to form a uniform distribution of ions at a selected depth inthe substrate material for film transfer processes.

2. Present Plasma Immersion Systems

FIG. 2 is a simplified overview of a plasma treatment system 200 forimplanting particles according to an embodiment of the presentinvention. This diagram is merely an illustration and should not limitthe scope of the claims herein. One of ordinary skill in the art wouldrecognize other variations, modifications, and alternatives. For easyreading, some of the reference numerals used in FIG. 1 are used in FIG.2 and others. In a specific embodiment, system 200 includes a vacuumchamber 14 having a vacuum port 18 connected to a vacuum pump (notshown). The system 200 includes a dielectric window 26 vacuum sealed byo-rings 30 and attached by removable clamps 34 to the upper surface 22of the vacuum chamber 14. Removably attached to the dielectric window 26is an rf plasma source 40, in one embodiment having a helical or pancakeantennae 46 located within an outer shield/ground 44. Other embodimentsof the antennae using capacitive or inductive coupling may be used. Therf plasma source can be operated at 13.56 MHz, and other frequencies.Cooling of each antenna is accomplished by passing a cooling fluidthrough the antenna. Cooling is typically required only at higher power.The window 26 without attached rf plasma sources 40 is usable as aviewing port into the chamber 14. The removability of each plasma source40 permits the associated dielectric window 26 to be cleaned or theplasma source 40 replaced without the vacuum within the system 10 beingremoved.

Although a glass window is used in this embodiment, other dielectricmaterials such as quartz or polyethylene may be used for the windowmaterial. Antenna 46 is connected to an rf generator 66 through amatching network 50, through a coupling capacitor 54. Antenna 46 alsoincludes a tuning capacitor 58 connected in parallel with its respectiveantenna 46. The tuning capacitor 58 is controlled by a signal D from acontroller 62. By adjusting the tuning capacitor 85, the output powerfrom the rf antenna 46 can be adjusted to maintain the uniformity of theplasma generated. Other tuning means such as zero reflective powertuning may also be used to adjust the power to the antennae. In oneembodiment, the rf generator 66 is controlled by a signal E from thecontroller 62. In one embodiment, the controller 62 controls the powerto the antennae 46 by a signal F to the matching network 50.

The controller 62 adjusts the tuning capacitor 58 and the rf generator66 in response to signals A, B, and C. Signal A is from a sensor 70(such as a Real Power Monitor by Comdel, Inc., Beverly, Mass.)monitoring the power delivered to the antennae 46. Signal B is from afast scanning Langmuir probe 74 directly measuring the plasma density.Signal C is from a plurality of Faraday cups 78 attached to a substratewafer holder 82. The Langmuir probe 74 is scanned by moving the probe(double arrow I) into and out of the plasma. With these sensors, thesettings for the rf generator 66 and the tuning capacitors 58 may bedetermined by the controller prior to the actual use of the system 200to plasma treat a substrate. Once the settings are determined, theprobes are removed and the wafer to be treated is introduced. In anotherembodiment of the system, the probes are left in place during processingto permit real time control of the system. In such an embodiment using aLangmuir probe, care must be taken to not contaminate the plasma withparticles evaporating from the probe and to not shadow the substratebeing processed. In yet another embodiment of the system, thecharacteristics of the system are determined at manufacture and thesystem does not include a plasma probe.

In a preferred embodiment, a magnetic field is applied to the plasma inthe vacuum chamber 14. In a specific embodiment, an electro-magneticsource 207 is applied to an upper vessel portion and an electro-magneticsource 209 is applied to a lower vessel portion. These sources andothers shape the plasma to form magnetic field lines 211 and 213, whichpush or shape the plasma away from walls of the vessel. In a specificembodiment, the electro-magnetic source can be a conductor such as aplurality of wires or cables, which conduct current. Alternatively, themagnetic source can be a single conductive member that carries electriccurrent, which forms a magnetic field. In a specific embodiment, theconductor is a plurality of wires, which are wrapped around theperiphery of the vessel. The wires are suitably constructed such thatthey carry enough electric current to influence the plasma in thevessel. In one embodiment, the wires are a plurality of insulated wiresthat are wrapped around a periphery of the vessel. The insulated wireseach include a conductive core.

A power source(s) supplies direct current to the magnetic sources.Magnetic source 207 couples to a power source 215, which supplies directcurrent in one direction to the wires. Magnetic source 209 couples topower source 215, which supplies direct current in another direction(which is opposite of magnetic source 207). The power source can be anysuitable power source such as a DC power supply product (max 50 V or max50 delta made by a company called Hewlett Packard, but is not limited.The power source is capable of supplying direct current to about 50 ampsup to about 50 volts. A power rating of about 2,500 watts or greater isalso desirable, but is not limiting.

In a specific embodiment, a combination of the rf plasma source 40 andelectro-magnetic sources 207, 109 create “cusp” regions 217, 218, and219. Here, the combination of the sources are operated in a manner whichmaintains a substantial portion of the plasma to be confined within aspatial area away from the walls. By way of this confinement,recombination of the plasma species near the walls is reduced. Thecombination of the sources also provide for a higher plasma density. Thehigh density plasma uses inductive coupling from the rf plasma sourceand uses the magnetic sources 207 and 209 to shape the plasma. Theshaped plasma also has a much higher energy and density than the plasmacreated by only the rf plasma source. The high density plasma can beused for a number of applications including, plasma immersion ionimplantation and others. In some embodiments, a cooling source (notshown) can be applied near an outer wall of the chamber near cusp region218, which is often concentrated with electrons. The electrons createadditional heat near the chamber wall that should be removed by way ofthe cooling source.

Controller 62 is used to control power to the magnetic sources 207 and209. Controller 62 includes output G, which selectively adjusts theamount of direct current provided to magnetic source 207. Output G canalso selectively adjusts the amount of direct current provided tomagnetic source 209. The output can be determined by way of signal Bfrom a fast scanning Langmuir probe 74 directly measuring the plasmadensity. Alternatively, the output can be determined by signal C, whichis from a plurality of Faraday cups 78 attached to a substrate waferholder 82. The Langmuir probe 74 is scanned by moving the probe (doublearrow I) into and out of the plasma. With these sensors, the settingsfor power supply 215 and for the rf generator 66 and the tuningcapacitors 58 may be determined by the controller prior to the actualuse of the system 200 to plasma treat a substrate. Once the settings aredetermined, the probes are removed and the wafer to be treated isintroduced. In another embodiment of the system, the probes are left inplace during processing to permit real time control of the system. Insuch an embodiment using a Langmuir probe, care must be taken to notcontaminate the plasma with particles evaporating from the probe and tonot shadow the substrate being processed. In yet another embodiment ofthe system, the characteristics of the system are determined atmanufacture and the system does not include a plasma probe.

Referring to FIG. 3, the configuration of plasma sources 40 may be suchthat a plurality of physically smaller plasma sources 40 produce auniform plasma over an area greater than that of sum of the areas of theindividual sources. In the embodiment of the configuration shown,four-inch diameter plasma sources 40 spaced at the corners of a squareat six-inch centers produce a plasma substantially equivalent to thatgenerated by a single twelve inch diameter source. Therefore, byproviding a vacuum chamber 14 with a plurality of windows 26, thevarious configurations of plasma sources 40 may be formed to produce auniform plasma of the shape and uniformity desired. Antennae such asthose depicted do not result in rf interference between sources whenproperly shielded as shown.

The Faraday cups 78 used to measure the uniformity of the field and theplasma dose, in one embodiment, are positioned near one edge in thesurface of the wafer holder 82, which is shown in FIG. 4. The flat edge86 of wafer 90 is positioned on the wafer holder 82 such that Faradaycups 78 of the wafer holder 82 are exposed to the plasma. In this waythe plasma dose experienced by the wafer 90 can be directly measured.Alternatively, a special wafer 90′, as shown in FIG. 4A, is fabricatedwith a plurality of Faraday cups 78 embedded in the wafer 90′. Thisspecial wafer 90′ is used to set the rf generator 66 and the tuningcapacitors 58 to achieve the desired plasma density and uniformity. Oncethe operating parameters have been determined, the special wafer 90′ isremoved and the wafers 90 to be processed are placed on the wafer holder82.

Referring to FIG. 5, in another embodiment, a quartz window 100 is notdirectly attached to the vacuum chamber 14, but instead encloses one endof the shield 44 of the plasma source 40′. In this embodiment, a tube104 attached to an opening 108 in the quartz window 100 provides a gasfeed to form a plasma of a specific gas. In this case, the plasma source40′ is not attached to a window 26 in the wall of the vacuum chamber 14,but is instead attached to the vacuum chamber 14 itself. Such plasmasources 40′ can produce plasmas from specific gases as are generallyrequired by many processes.

Several such plasma sources 40′ can be aligned to sequentially treat awafer 90 with different plasmas as in the embodiment of the in linesystem shown in FIG. 6. In this embodiment, wafers 90 are moved by aconveyor 112 through sequential zones, in this embodiment zones I andII, of a continuous processing line 114. Each zone is separated from theadjacent zones by a baffle 116. In one embodiment, the gas in zone I isfor a cleaning processing, while the gas in zone II is hydrogen used inimplanting. In another embodiment, a cluster tool having load-locks toisolate each processing chamber from the other chambers, and equippedwith a robot includes the rf plasma sources 40 of the invention forplasma CVD, plasma etching, plasma immersion ion implantation, ionshower, or any non-mass separated ion implantation technique.

A magnetic field is applied to plasma in the vacuum chamber 114. In aspecific embodiment, an electro-magnetic source 607 is applied to anupper vessel portion and an electro-magnetic source 609 is applied to alower vessel portion. These sources shape the plasma to form magneticfield lines 611 and 613, which push and shape the plasma away from wallsof the vessel. In a specific embodiment, the electro-magnetic source canbe a single or multiple conductors such as a plurality of wires orcables, which conduct current. In a specific embodiment, the conductoris a plurality of wires, which are wrapped around the periphery of thevessel. The wires are suitably constructed such that they carry enoughelectric current to influence the plasma in the vessel. In oneembodiment, the wires are a plurality of insulated wires that arewrapped around a periphery of the vessel. The insulated wires eachinclude a conductive core. Magnetic source 607 couples to a power source615, which supplies direct current in one direction to the wires.Magnetic source 609 couples to power source 615, which supplies directcurrent in another direction (which is opposite of magnetic source 607).The power source can be any suitable power source such as a DC powersupply product made by a company called Hewlett Packard, but is notlimited.

In a specific embodiment, a combination of the rf plasma source 40′ andelectro-magnetic sources 607, 609 create “cusp” regions 617 and 619.Here, the combination of the sources are operated in a manner whichmaintains a substantial portion of the plasma confined to a spatial areaaway from the walls, which prevents recombination of plasma species nearthe walls. The combination of the sources also provide for a higherplasma density. The high density plasma uses inductive coupling from therf plasma source and uses the magnetic sources 607 and 609 to shape theplasma. The shaped plasma also has a much higher energy and density thanthe plasma created by only the rf plasma source. The high density plasmacan be used for a number of applications including, plasma immersion ionimplantation and others.

FIG. 7 depicts an embodiment of the system of the invention using twoplasma sources. In this embodiment each source is an inductive pancakeantenna 3-4 inches in diameter. Each antenna 46 is constructed of a ¼inch copper tube and contains 5-6 turns. Each antenna 46 is connected toa matching network 50 through a respective 160 pf capacitor. Thematching network 50 includes a 0.03 μH inductor 125 and two variablecapacitors 130, 135. One variable capacitor 130 is adjustable over therange of 10-250 pf and the second capacitor 135 is adjustable over therange of 5-120 pf. The matching network 50 is tuned by adjusting thevariable capacitor 130, 135. The matching network 50 is in turnconnected to an rf source 66 operating at 13.56 MHz or other suitablefrequencies. Electro magnetic sources 140, 145 are positioned around thecircumference of the chamber. These sources include a conductive wire(s)140, which is wrapped around a lower portion of the chamber. The wires140 provide current in one direction. Conductive wire(s) 145 is wrappedaround an upper portion of the chamber. The wires 145 provide current inanother direction, which is opposite of the direction of wires 140. Thecombination of these wires and the rf source provides a high densityplasma discharge.

While the above description is generally described in a variety ofspecific embodiments, it will be recognized that the invention can beapplied in numerous other ways. For example, the improved plasma sourcedesign can be combined with the embodiments of the other FIGS.Additionally, the embodiments of the other FIGS. can be combined withone or more of the other embodiments. The various embodiments can befurther combined or even separated depending upon the application.Accordingly, the present invention has a much wider range ofapplicability than the specific embodiments described herein.

In a specific embodiment, the present invention provides a methodaccording to an embodiment of the present invention. The method can bebriefly outlined as follows:

1. Provide a work piece (e.g., silicon wafer);

2. Introduce the work piece into a vacuum chamber;

3. Evacuate the vacuum chamber to a first pressure;

4. Introduce a gas (e.g., hydrogen) into the vacuum chamber;

5. Ignite the gas to form a plasma using an rf power source;

6. Maintain the plasma using the rf power source;

7. Pump down the chamber to a second pressure;

8. Apply magnetic field onto plasma;

9. Form cusp(s) with plasma;

10. Form enhanced plasma mode;

11. Apply bias between plasma and work piece;

12. Accellerate particles from plasma toward work piece;

13. Form a concentration of particles at a selected depth in the workpiece;

14. Purge chamber;

15. Remove implanted work piece; and

16. Perform remaining fabrication steps, as desired.

The above sequence of steps is used to provide a method according to thepresent invention. The present method includes steps of providing a workpiece, forming a high density plasma, and accellerating particles fromthe plasma into a work piece. By way of substantially pure plasmaspecies, the present invention provides a substantially uniform implantfor a variety of processes such as layer transfer techniques. Furtherdetails of the present method are shown by way of reference to the FIGS.below.

FIG. 8 is a simplified flow diagram of a method 800 for implantingparticles according to an embodiment of the present invention. Thediagram is merely an example and should not limit the scope of theclaims herein. One of ordinary skill in the art would recognize othervariations, modifications, and alternatives. As shown, the method beginsat start, which is step 801. A work piece (e.g., silicon wafer) isplaced into the chamber. In some embodiments, a robot or transfer armperforms the placement step. The chamber is pumped down (step 805),which evacuates the chamber. Once the chamber is evacuated, a highdensity plasma is formed (step 807). The high density plasma is formedusing any one of the techniques described herein, as well as others. Ina preferred embodiment, the high density plasma is substantially purehydrogen H₁+, which is described herein. The substantially pure hydrogenhas a positive ionic charge.

To implant these particles into the work piece, a negative bias isapplied to the work piece. In one embodiment, the negative bias ispulsed. Alternatively, the negative bias is a straight D.C. current or aquasi D.C. current, which is made of a plurality of pulses. The biaspulls the particles form the plasma into the work piece. That is, thevoltage bias accelerates the particles through a surface of the workpiece to a selected depth within the work piece. Once the particles areintroduced into the work piece, additional processing can be performed.These processes include, among others, a layer transfer process such asa controlled clevage process, which is described in U.S. Ser. Nos.09/026,115; 09/026,027; and 09/026,034, commonly assigned, and which areall incorporated by reference herein. Additional layer transfersynthesis of SOI materials processes such as the Smart Cut™ process ofSoitec of France.

FIG. 8A is a simplified flow diagram of a method 814 for igniting a highdensity plasma according to an embodiment of the present invention. Thediagram is merely an example and should not limit the scope of theclaims herein. One of ordinary skill in the art would recognize othervariations, modifications, and alternatives. The present method beginswith a start step (step 815). The present method includes, among othersteps, pumping down or evacuating (step 817) the vacuum chamber to afirst pressure. The rf power source is applied which ignites (step 819)and maintains an inductively coupled plasma. The chamber is then pumpeddown or evacuated to a second pressure, which is lower than the firstpressure, where the magnetic field is applied (step 823). The magneticfield is applied in the manner described herein as well as others. Insome embodiments, the magnetic field is applied before step 817 or anyother time, when it is convenient. The combination of the appliedmagnetic field and the rf power provides an enhanced plasma, which issubstantially a single isotope, e.g., H₁+. The substantially pure plasmacan be used for a variety of processes such as the ones describedherein, as well as others.

Although the above has been generally described in terms of specificmethods, the present invention can also be applied to a variety of otherplasma processes. For example, the present invention can be applied to aplasma source ion implantation system using a plasma immersion ionimplantation system or any non-mass separated system such as ion showeror the like. Accordingly, the above description is merely an example andshould not limit the scope of the claims herein. One of ordinary skillin the art would recognize other variations, alternatives, andmodifications.

Experiments

To prove the principles and operation of the present invention,experiments were performed. In these experiments, a chamber having adiameter of about thirty inches and a height of about thirty six incheswas used. The chamber was made of stainless steel. Waban Technology,Inc. of Massachusetts (now Silicon Genesis Corporation) provided thechamber. A single inductive coil was placed on an upper region of thechamber. The inductive coil was placed on a substantially planar window,which was concentrically aligned overlying a susceptor region of thechamber. The inductive coil used a ¼-inch diameter copper coil, whichwas wrapped about FIVE times about a center region. The inner region ofthe inductive coil was grounded while the outer region of the coil wassubjected to rf power of 13.56 MHz. The overall diameter of theinductive coil was about twelve inches. The power supplied to the coilwas maintained at about 4.5 kilo-watts during operation. The inductivecoil was made of a copper material and had cooling fluid running in thecoil to prevent the coil from beating up excessively. A silver plate wascoupled to the coil to enhance cooling.

Magnetic sources were constructed by way of insulated wires. A pluralityof insulated wires were wrapped surrounding the circumference of thechamber. A first group of wires were wrapped in an upper circumferenceregion of the chamber. About 15 to 20 wraps were made using these wires.In a center region of the chamber, which is above the susceptor, asecond group of wires were wrapped about the circumference region of thechamber. About 15 to 20 wraps were made using these wires. A powersource was applied to each of the groups of wires. A direct current(“D.C.”) power source of about 5 volts and about 40 Amps. was applied tothe top group of wires. A D.C. power source of about 5 volts and about40 Amps. was applied to the bottom group of wires. Details of applyingthe proper voltage and current are described in more detail below.

A hydrogen gas source was applied to provide hydrogen gas into thechamber. The hydrogen gas source was semiconductor grade (99.9995%)purity hydrogen gas. The gas entered the chamber at a flow rate of 20sccm, which was at a temperature of room (or ambient) and pressure of afew milli-torr. A mass flow controller was used to selectively introducethe hydrogen gas into the chamber. The mass flow controller was made bya company called MKS, but is not limited. The mass flow controllerselectively allowed hydrogen gas to enter into the chamber.

In operation, a work piece such as a blank 8-inch silicon wafer isplaced into the chamber. A vacuum pump evacuates the chamber. The vacuumis generally maintained such that the chamber has a pressure of about0.5 milli-torr and less during processing. Of course the particularpressure used depends highly upon the application. The vacuum pump canbe any suitable unit such as a Turbo Molecular pump made by a companycalled Varian, but is not limited to such a pump. Hydrogen gas isallowed to enter the chamber. Next, rf power is applied to the ignitethe plasma. The rf power is at about 4 kW. A glow discharge can be seenthrough a glass viewing window on the side of the vacuum chamber. Themixture of the hydrogen bearing particles are measured.

A mass spectrometer system was used to measure the relativeconcentrations of hydrogen bearing particles. In the present example, amass spectrometer made by a company called Hiden of England was used.Here, a probe was placed into the chamber, as shown. The probe was usedat two locations in the chamber to sense the type of hydrogen in theplasma. The probe was inserted into the chamber at a first position,which is against the wall region of the chamber. A measurement was takenat the first position. Next, the probe was moved to a second location inthe chamber, as shown. A measurement was taken at the second position.Table 1 lists the mixture of hydrogen bearing particles for two trials.The first trial measures hydrogen for a source where only an rf sourceis applied. The second trial measures hydrogen for a source thatincludes the rf source and the magnetic field source.

TABLE 1 List of Concentrations of Hydrogen Power Source(s) Hydrogen (1)Hydrogen (2) Hydrogen (3) Rf source <1% 60% 40% Rf source + field 99.96%<1% <1%

As seen in Table 1, the concentration of hydrogen bearing particlesinclude hydrogen (1) (e.g., H₁+), hydrogen (2) (e.g., H₂+ and H₂) andhydrogen (3) (e.g., H₃+). By way of inductive coupling from the rf powersource, the hydrogen bearing particles include H(1), H(2), and (3). Thepresence of all three forms of hydrogen are believed to be based uponrecombination of certain species of hydrogen at, for example, a wallregion. The plasma density using inductive coupling is about 5×10⁹ions/cubic centimeter.

When the pressure is about 1 milli-torr, the magnetic field is appliedto the chamber by way of the D.C. power source(s). The plasma dischargetransforms into a state that is dominated by H(1). An inspection of theillumination of the hydrogen discharge through the glass window revealsa higher intensity of light illuminating from the plasma. Theillumination is much brighter (i.e., the color turned from blue tomagenta) than the plasma discharge made by way of only the rf source.

The relative concentrations of hydrogen bearing particles have alsochanged. Table 1 lists the relative change, where hydrogen (1) is nowgreater than 99%, hydrogen (2) is less than 0.05%, and hydrogen (3) isless than 0.001%. Accordingly, the plasma discharge becomessubstantially hydrogen (1), which we call the “protonic mode” ofhydrogen.

FIG. 9 illustrates a relative measurement of the hydrogen bearingparticles. The hydrogen bearing particles include at least H(1), H(2),and H(3). As shown, the left axis illustrates intensity of hydrogenbearing particles in units of counts/second (“SEM”). The lower axisillustrates mass of the hydrogen bearing particles in atomic mass unit(herein “AMU”). The peak near the AMU of value 1 reveals H(1). Thesmaller peaks near the AMU values of 2 and 3 refer, respectively, toH(2) and H(3). A simple calculation made using the FIG. shows an H(1)concentration relative to H2 and H3 of 99.96% purity, which is believedto be significant. It is believed that present conventional techniquescannot achieve such high purity by way of conventional plasma processingtools and the like.

To implant the hydrogen bearing particles, a voltage bias (i.e., quasiDC pulse) is applied between the plasma and the work piece. The workpiece is maintained at a voltage potential of about less than 50 kV. Theplasma source has an applied voltage potential of about a few tens ofvolts. By way of the differential in voltage between the work piece andthe plasma discharge, the hydrogen bearing particles are acceleratedinto the surface of the work piece. The hydrogen bearing particlesaccelerate through the surface of the work piece and rest at a selecteddepth underneath the surface of the work piece. It is believed thatsince the hydrogen bearing particles are substantially a single species,a substantial portion of the plasma implants into the substrate in asimilar manner. By way of this manner, a substantially uniform implantis achieved.

By way of the present plasma source, a high degree of uniformity in theimplant is achieved. FIG. 10 is a simplified profile 900 of an implantaccording to the present experiment. As shown, the particles counts weremeasured by way of a Langmuir probe. The probe measured a substantialuniform distribution of implanted particles that were measured using theprobe. As shown, the concentration centered around 2.9×10¹⁶ ions/r³. Theconcentration does not substantially vary about the region, which isoccupied by a substrate. The substrate region is defined outside of the28 centimeter position, where the 40 centimeter position defines acenter portion of the substrate.

In a specific embodiment, the present invention achieves other ionconcentrations, which enhance plasma immersion ion implantation. Asmerely an example, the hydrogen ion concentration is greater than about1×10¹⁰ ions/cm³, or greater than about 5×10¹⁰ ions/cm³, or greater thanabout 5×10¹¹ ions/cm³, or greater than about 1×10¹² ions/cm³.Conventional ICP sources yielded no greater than about 1×10⁹ hydrogenions/cm³ using similar plasma tools. Accordingly, the present plasmasource yields about 100 times or 200 times higher plasma densities thanconventional tools.

Although the above has been generally described in terms of a PIIIsystem, the present invention can also be applied to a variety of otherplasma systems. For example, the present invention can be applied to aplasma source ion implantation system. Alternatively, the presentinvention can be applied to almost any plasma system where ionbombardment of an exposed region of a pedestal occurs. Accordingly, theabove description is merely an example and should not limit the scope ofthe claims herein. One of ordinary skill in the art would recognizeother variations, alternatives, and modifications.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. A plasma treatment method comprising: forming anrf plasma discharge in a vacuum chamber, said plasma discharge includingan inductive coupling structure, said inductive coupling structurecomprising a first cusp region at a first end of said structure and asecond cusp region at a second end of said structure; wherein said firstcusp region is provided by a first electro-magnetic source and saidsecond cusp region is provided by a second electro-magnetic source; andwherein said first electro-magnetic source and said secondelectro-magnetic source confining a substantial portion of said rfplasma discharge to a region away from a wall of said vacuum chamber. 2.The method of claim 1 wherein said rf plasma discharge is provided by asingle coil disposed overlying an upper surface of said vacuum chamber.3. The method of claim 1 wherein said rf plasma discharge is provided bya plurality of coils, each of said coils being disposed overlying anupper surface of said vacuum chamber.
 4. The method of claim 2 furthercomprising a tuning circuit coupled to said single coil.
 5. The methodof claim 1 wherein said first cusp is toward said a rf plasma source. 6.The method of claim 1 wherein said second cusp region is toward saidsusceptor.
 7. The method of claim 1 further comprising applying avoltage bias between said rf plasma discharge and a workpiece tointroduce partices in said rf plasma discharge into a surface of saidworkpiece.
 8. The method of claim 1 further comprising providing adirect current from a direct current power supply to said firstelectro-magnetic source.
 9. The method of claim 8 further comprisingproviding a direct current from a direct current power supply to saidsecond electro-magnetic source.
 10. The method of claim 9 wherein saidfirst electro-magnetic source is coupled to said direct current powersupply to current that flows in a first direction.
 11. The method ofclaim 10 wherein said second electro-magnetic source is coupled to saiddirect current power supply to supply current that flows in a seconddirection, said second direction being opposite of said first direction.12. The method of claim 1 further comprising feeding hydrogen gas intosaid vacuum chamber to form said rf plasma discharge comprising hydrogenbearing particles.
 13. The method of claim 1 wherein said rf plasmadischarge is a hydrogen bearing plasma.
 14. The method of claim 1wherein said rf plasma discharge is substantially a hydrogen bearingplasma of H₁ ⁺ particles.
 15. The method of claim 1 further comprisingproviding a workpiece on a susceptor in said vacuum chamber.
 16. Themethod of claim 11 further comprising accelerating particles from saidrf plasma discharge into and through a surface of a work piece to aselected depth underlying said surface of said work piece.